Metathesis catalysts have been previously described by for example, U.S. Pat. Nos. 5,312,940, 5,342,909, 5,728,917, 5,750,815, 5,710,298, and 5,831,108 and PCT Publications WO 97/20865 and WO 97/29135 the contents of each of which are incorporated herein by reference. These publications describe well-defined single component ruthenium or osmium catalysts that possess several advantageous properties. For example, these catalysts are tolerant to a variety of functional groups and generally are more active than previously known metathesis catalysts. The ruthenium and osmium complexes disclosed in these patents all possess metal centers that are formally in the +2 oxidation state, have an electron count of 16, and are pentacoordinated. These complexes possess the following general structure, and are useful as initiators in the ring-opening metathesis polymerization (ROMP) of strained cycloolefins, such as norbornene, dicyclopentadiene, tricyclopentadiene, and functionalized norbornenes. The ring-opening metathesis polymerization (ROMP) of and addition polymerization of polycyclic olefins is depicted generally in the following reaction schemes: 
These compounds are also useful entry complexes for other metathesis reactions, including, for example, addition polymerization metathesis, ring-closing metathesis (RCM), acyclic diene metathesis (ADMET), cross-metathesis (CM) and degenerative olefin metathesis (OM).
In particular, U.S. Pat. Nos. 5,312,940 and 5,342,909 describe the synthesis of Ru(X)(X1)(L)(L1)(═C((R)(R1)) and their related ring-opening metathesis polymerization (ROMP) activity. In these patents, L and L1 are both Lewis base ligands. Further, in each of these patents the preferred Lewis base is triphenylphosphine. Subsequently, U.S. Pat. No. 5,922,863, the contents of which are incorporated herein by reference, discloses that the substitution of triarylphosphine by the more basic secondary alkyl or cycloalkylphosphines results in improved olefin metathesis activity.
It is now well recognized that one of the more active ruthenium initiator species for olefin metathesis contains a saturated or an unsaturated N- heterocyclic carbene (NHC) moiety. The increased activity of this moiety is reported in, for example, PCT Publications WO 99/51344, WO 00/15339, WO 00/15339, and WO 00/58322, the contents of each of which are incorporated herein by reference.
To date, the preferred initiators for the ROMP of dicyclopentadiene are those possessing two tertiary phosphine ligands (PR3) and those possessing one NHC and one tertiary phosphine (PR3), i.e., 
A representative Initiator A can be prepared using a “one-pot method” in almost quantitative yield from [Ru(COD)Cl2]n and tricyclopentylphosphine in the presence of hydrogen and 3-chloro-3-methyl-1-butyne. A representative Initiator B is prepared from RuCl2(PCy3)2(═CHPh) (prepared from RuCl2(PPh3)3 and phenyldiazomethane and the subsequent addition of tricyclohexylphosphine) via a 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene for tricyclohexylphosphine ligand exchange in toluene at about 80° C. Under typical ROMP conditions, Initiator A is capable of polymerizing DCPD effectively at generally about 7500:1 (DCPD:Ru (mole ratio))and further conversion may be accomplished through additional post curing of the object. Alternatively, Initiator B can be employed at levels up to about 100,000:1 (DCPD:Ru (mole ratio)) and does not require a post cure step. Currently, it is more cost effective to manufacture Initiator A in place of Initiator B, but the high catalyst efficiency is not reached, i.e., conversion of monomer to polymer, and posturing of polyDCPD parts is commonplace. One disadvantage to the use of well-defined alkylidene catalysts such as Initiator A and B is that they initiate polymerization (or olefin metathesis) immediately upon contact with a metathesizable monomer. Another drawback of the Initiator B type species is that such species are sensitive to the reaction temperature in comparison to the Initiator A type, so that a reaction medium of polycyclic olefin gels or “sets up” more rapidly. The high activity of Initiator B is preferred over Initiator A, but the processability of Initiator A is preferred over Initiator B. Initiator B is also more resistant to atmospheric (oxygen and water), temperature, and monomer impurities than Initiator A.
It has been reported in the literature, in for example, M. A. Sanford, M. Ulman, and R. H. Grubbs, J. Am. Chem. Soc, 2001, 123, 749-750, the contents of which are herein incorporated by reference, that the high activity for the NHC carbene coordinated initiator (Initiator B), which had been attributed to its ability to promote phosphine dissociation, instead appears to be due to the improved selectivity for binding π-acidic olefinic substrates in the presence of a σ-donating free phosphine. Also, the addition of Lewis bases to Initiator A can further slow the initiation process of the polymerization because of the competition between the olefin and the Lewis base.
Transition metal derivatives and initiator precursors useful in the addition polymerization of norbornene and substituted norbornenes (“polycyclic olefins”) are described in U.S. Pat. Nos. 5,705,503; 5,571,881; 5,569,730; and 5,468,819 and in PCT Publications WO 97/20871; WO 00/34344; WO 00/20472; WO 99/14256; WO 96/37526; WO 97/20871; WO 97/33198; WO 95/14048; and WO 97/33198, the contents of each of which are herein incorporated by reference.
The thermal conversion of 1,3-diphenyltrichloromethylimidazoline is shown in Scheme 2: 
Similarly, 1,3-diphenyl-2-alkoxyimidazolidine, i.e., 2-methoxy-1,3-diphenylimidazolidine and 2-(benzyloxy)-1,3-diphenyl-imidazolidine, can lose alcohols (anomalous α-elimination) upon heating to give 1,3-diphenylimidazolidin-2-ylidene.
In addition, in-situ deprotection to perform a ligand switch at a metal occurs during the thermal deprotection of 1,3-diphenyl-2-trichloromethylimidazolidine in refluxing xylene in combination with di-μ-chlorobis(triethylphosphine)diplatinum to generate trans-dichloro(1,3-diphenylimidazolidin-2-ylidene)(triethylphosphine)platinum(II). Similarly, bis(1,3-diaryl) and bis(1,3-diaralkyl)-imidazolidinylidene compounds (bis-NHC carbene precursors) may be employed in the generation of ruthenium, platinum, and palladium compounds containing an imidazolidin-2-ylidene moiety.
In addition, there have been some ligand exchange reactions based, e.g., triarylphosphine substitution by imidazolidine, at a metal center employing “transient” or “in-situ”-generated, ether protected, substituted and unsubstituted imidazolidines, i.e., 
Further, Grubbs described in Organic Letters (1999), 1(16), 953-956, that the alkoxy-protected NHC species did not react with benzylidene ruthenium complexes in solvent at ambient temperature; however, they readily reacted with RuCl2(PR3)2(═CHR) when deprotected in situ by heating to 60-80° C. However, the isolation of these alkylidenes generally requires air-free, anhydrous conditions, and multiple purifications to remove the displaced trialkylphosphine.
R. H. Grubbs and M. Scholl describe the method of making compounds of the following formula in PCT publication WO 00/71554, the contents of which are herein incorporated by reference: 
The ruthenium or osmium complexes employed were of the identity MCl2L2(═C(R)(R1), where L is a Lewis base. The ether-based imidazolidine is prepared as shown in the following scheme: 
However, in these systems, the ether is not isolated, but used in-situ. The deprotection step occurs most efficiently when heating the ether derivative and the free imidazolidine NHC is generated and replaces the ligand at the metal complexes within about ten minutes. Representative examples of suitable bases include t-BuOK/THF, t-BuONa/THF, and NaOCH3/CH3OH.
The in situ preparation of a highly active N-heterocyclic carbene-coordinated olefin metathesis catalyst has been described by Morgan and Grubbs, Org. Letters. (2000), 2(20), 3153, the contents of which are incorporated herein by reference, for cross and ring-closing metathesis reactions. The paper disclosed that the high activity ruthenium alkylidene initiators could be generated without requiring prior isolation of the catalyst. However, the activation of this in situ catalyst with HCl or other phosphine scavengers was useful to improve the reaction times required for high conversions and to overcome the phosphine inhibition. Furthermore, the NHC precursor in this system was not isolated, but generated in solvent, e.g., 
It would therefore be desirous to be able to convert a less active (i.e., slower to initiate) system, such as Initiator A, to a higher activity system, i.e., Initiator B, so that at the end of a polymerization the most active species is present in the system. Such reactions would be expected to be slow at their start allowing improved pot life, and, yet, at the end of the reaction, allow for excellent monomer to polymer conversion. Further, the more thermally stable Initiator B species would be longer lived at the high temperatures associated with the ROMP of polycyclic olefins. Additionally, it is of benefit to have a synthetic method to generate species such as Initiator B which (i) uses readily available ingredients, (ii) reduces the number of synthetic steps, (iii) eliminates the need for a phosphine exchange, (iv) eliminates the separation of by-products, and (v) yields an initiator with the appropriate ligand set in high yield.
The invention overcomes the shortcomings of the prior art by providing a method which moderates a cyclic olefin polymerization reaction (ROMP or Addition, for example) through the use of a protected NHC, while obtaining excellent monomer to polymer conversion. The invention accomplishes this by using the polymerization exotherm generated by a ROMP initiator or addition initiator to be the source of energy for deprotecting a NHC—X2—Y reagent which, in turn, enhances the activity of the initial polymerization (ROMP or Addition Polymerization, for example) initiator. The reagent described herein is an air-stable, isolable, and deprotectable NHC reagent, i.e., NHC—X2—Y. In addition, the invention provides new NHC ruthenium alkylidene initiator identities, and new synthetic routes to ruthenium initiators.
In particular, the invention is related to the in-situ preparation of NHC metal carbene metathesis catalyst species in polycyclic olefin formulations, which exhibit comparable activity to those previously described. Yet the inventive methods do not require extensive purification under rigorously air- and moisture-free conditions nor the removal of free phosphine ligand and are prepared from stable and isolable starting complexes.